1. Field of the Invention
The present invention relates to a drum (rotating body) for disposing a sheet-type member on a circumferential locus of a predetermined radius centering around a rotation axis.
2. Description of the Related Art
Conventionally, some image exposure apparatuses, which subject printing plates to image exposure, wind a printing plate onto a rotating drum and irradiate the printing plate with a light beam in accordance with image data while rotating the printing plate integrally with the rotating drum, so as to scan-expose the printing plate.
When the printing plate is wound onto the rotating drum, the printing plate is fixed onto the rotating drum by chucks so that both edges of the printing plate on a peripheral surface of the rotating drum are nipped between the chucks and the peripheral surface of the rotating drum.
Namely, a chuck which corresponds to one edge of the printing plate on the peripheral surface of the rotating drum (e.g., a leading edge thereof in a direction it is wound) is attached in advance at a predetermined position on the rotating drum, and another chuck which corresponds to the other edge of the printing plate (e.g., a trailing edge thereof in a direction it is wound) is attached at a position on the rotating drum in accordance with the size of the printing plate after the printing plate has been wound onto the rotating drum.
The drum used in the above-described image exposure apparatus has a peripheral surface in a cylindrical shape. The printing plate is brought into tight contact with the peripheral surface of the drum in order to determine a position of the printing plate in a thickness direction, so that the printing plate can correspond to a depth of focus of a light beam for scan-exposure.
However, in the conventional drum, at least the peripheral surface thereof needs to have an unfolded area which is larger than an area of the printing plate. Therefore, when a large-sized printing plate is used, a large-sized drum needs to be prepared. When the drum is enlarged, weight thereof is increased and rotation speed thereof is decreased. In order to realize a high-speed processing, a high-power driving system is required to prevent the decrease of the rotation speed.